Takehiko Ishihara

Chemical Degradation of Kerosene Diluent with Nitric Acid

Chemical degradation of kerosene diluent with nitric, acid was studied to clarify its effect on uranium distribution ratio and fission product retention in the presence of degradation products. The decontamination of fission products retained in degraded kerosene was also investigated. From the results of infrared spectrometry, it was recognized that nitro compounds, carboxylic acids, nitrate esters and nitroso compounds were formed as the main degradation products. The uranium distribution ratio in the extraction with TBP/degraded kerosene decreased with increasing concentration of nitric acid above 5 N, with rising temperature, and with increasing concentration of olefinic and aromatic hydrocarbons in the kerosene. It is suggested that the decrease of uranium distribution ratio may be due to the formation of carboxylic acids caused by the kerosene degradation. Some fission products, in particular 95Zr-95Nb and 131I, were retained in the organic phase, but 106Ru-106Rh did not remain after scrubbing with ...

Changes to Plutonium Extraction Behavior of TBP and Alkylamines through Irradiation

Changes to plutonium extraction properties brought about through irradiation of 30v/o TBP (Tri-n-butyl phosphate)/kerosene and 5v/o alkylamines/kerosene modified with lauryl alcohol were studied in such respects as extraction, scrubbing and stripping characteristics in nitrate media. The alkylamines examined were tri-n-octyl amine (TOA), N-cyclohexyl dilauryl amine (N-CHDLA) and Amberlite LA-2 (LA-2). These extractante were irradiated to the extent of 108R by 60Co γ-ray, prior to extraction. Marked changes with irradiation were observed in plutonium extraction performance with the TBP system tending to bring losses of plutonium, but very little change was found to occur with amine systems. Calculation of the single stage decontamination factors of fission products from plutonium proved that separation deteriorated with irradiation in the TBP system but hardly changed in the amine systems. From these findings, tertiary amines, especially N-CHDLA, can be judged superior to TBP for the direct recovery of plu...

The Effect of Hydrogen Bond Formation between Tri-n-Butyl Phosphate and Carboxylic Acid on Uranium Distribution

The distribution ratio of uranium between tri-n-butyl phosphate and water decreased with the addition of water-insoluble carboxylic acids such as benzoic, lauric, oleic and stearic acids at various concentrations of nitric acid. It is suggested that the decrease of uranium distribution ratio may be due to hydrogen bond formation between tri-n-butyl phosphate and carboxylic acid. It was indicated from infrared spectrometry that a strong hydrogen bond is formed between tri-n-butyl phosphate and carboxylic acid. In other cases, water-soluble carboxylic acids such as acetic, adipic and oxalic acids had no effect at all on the distribution ratio of uranium at various concentrations of nitric acid.

Effect of Temperature on the Extraction of Nitric Acid, Uranium and Fission Products with Tri-n-Octyl Amine

With the aim of finding an optimum temperature in fuel reprocessing with alkylamine, the effect of temperature on the extraction of nitric acid, uranium, zirconium and ruthenium with tri-n-octylamine was investigated in the temperature range between 20° and 60°C. In the neutralization reaction for the extraction of nitric acid the apparent equilibrium constants were determined for various temperatures. The average enthalpy change, average free energy change and average entropy change were found to be −16.3, −7.2 kcal/mol.deg and 8.0e.u., respectively. For the association reaction of nitric acid the average apparent enthalpy change was found to be 3.4kcal/mol-deg, which corresponds to hydrogen bond energy. The enthalpy change values were further determined for the extraction of uranium, zirconium and ruthenium, and found to be −1.3, 6.1 and 9.3 kcal/mol·deg. respectively. Within the temperature range studied, the lower regions of temperature appear to provide better separation of fission products from uran...

On Fission Product Retention of Degraded Kerosene with Nitric Acid

Determination of strong complexing species contained degradation products formed by the reaction of nitric acid on kerosene diluent was performed through: (I) observation of change in the absorbancy of nitroparaffines (at 1563 cm-1), of carboxylic acids (at 1694cm-1) and of nitrate esters (al 1640cm-1) against γ-activity of 95Zr-95Nb extracted into the degraded kerosenes; (2) separation of the main complexing species from the degraded kerosene by an acid-alkali treatment; and (3) nitration of oleic acid with nitrogen oxide gases and observation of change in its extractability for 95Zr-95Nb. It was conclusively established that nitroparaffines were among the main complexing species, and exhibited a strong retaining power on fission products, especially 95Zr-95Nb. Some possible retention mechanisms for fission products are proposed and discussed on the basis of tautomeric equilibria of nitroparaffines.